![]() ![]() I chose to operate in full step mode, which is fairly straightforward to implement and yields maximum torque. In this mode, two of the four motor coils are activated at a time, and the motor makes 32 steps per motor shaft revolution. From the video, you can see that the motors can be operated in various modes. There is an excellent video on these motors, 28BYJ-48 Stepper Motor and ULN2003 Driver Intro, on You Tube. I purchased 5 motors with driver boards from a US supplier on eBay. It didn't take long for me to come across the 28BYJ-48 5v stepper motor. These are readily available for hobbyists, complete with driver board to interface with microcontrollers such as Arduino. They are also quite inexpensive. What kind of motor could operate accurately at an unusual speed? I decided a stepper motor would work. My first thought along this line was to use one motor at the proper RPM for the seconds hand, and gears to drive the minutes and hours hands. But a divide by 100 gear train would require 4 sets of wheels and pinions to be compact. I decided to use a separate stepper motor for each hand. Not easy to find a synchronous motor like that. 864 of a standard second. With 100 metric seconds per revolution of the seconds hands, that makes 86.4 standard seconds per revolution, 60/86.4 =. My first thought was to use a 50 Hz synchronous motor. But doing the math reveals this to be problematic. There are 60*60*24 or 86,400 seconds per day in standard time, but 10*100*100 = 100,000 seconds per day in metric time. So a metric second is. I was asked to build an analog metric clock with hour, minute, and second hands that would run on Great Britain mains power. I have built clocks using 1 RPM synchronous motors, which run in step with 60 Hz 120v power. (If you do a search, you will discover so-called metric or decimal clocks for sale. But be careful - these clocks have what looks like a metric face (10 hour markings and numbering), but use a standard 12-hour mechanism, with 60 seconds per hour and 60 seconds per minute. Such a clock is not a metric clock at all. I have not been able to find a true metric clock for sale, other than antiques. If you find a modern one, please let me know.) Metric time, or French Revolutionary time, divides the day into decimal units. A day has 10 hours, an hour 100 minutes, and a minute 100 seconds. I was asked to build a metric, or decimal clock, as they are not readily available commercially.
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